A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on at least one circular disk having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read-write head that is positioned over a specific location of a disk by an actuator. A read-write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. A write head makes use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium.
Increasing areal density, a measure of the quantity of information bits that can be stored on a given area of disk surface, is one of the ever-present goals of HDD design evolution. As areal density increases, the read-write head generally needs to fly closer and closer to the disk surface. Flying height control systems are often used to fly the read-write head as close as possible to the magnetic-recording disk for effective operation of the head. For example, a heater element located in the head slider is typically used for thermal flying height control (TFC) which, for example, may be controlled by a preamplifier associated with the hard disk drive head stack assembly (HSA). By applying current to the heater, the surrounding slider material is caused to expand in response to the heat, which causes a bulge in the slider toward the disk thus reducing the flying height of the read-write head. TFC may be used to compensate for flying height fluctuations due to temperature, altitude, disk location, type of operation, and the like. Particularly during read operations, the heater causes the reader to be closer to the disk to increase the signal strength of the read-back signal read from the magnetic disk. Additionally, the heater may be used to cause the writer to be closer to the disk to increase the robustness of the magnetization written to the disk. Regardless of the operation for which TFC power may be applied, the TFC heater element has an associated time constant over which the desired slider bulge is generated, which depends on the head design, manufacturing tolerances, etc.
Any approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.